Not Applicable.
Not Applicable.
After each coating of a semi-conductor wafer, e.g. with an oxide layer, a tungsten layer or other metal layers, a processing has to take place in order to achieve planar surfaces. Otherwise, problems may occur with lithographic processes in form of focus failures of the UV stepper or in form of damages of the conductor paths. A common method in the semi-conductor industry for the planarization uses the so-called CMP process. This is a chemical-mechanical treatment by means of the fluid (slurry), whereby the chemically reactive part of the slurry has the objective to convert the material into a polishable condition. The slurry includes an abrasive in the form of colloidal abrasive small particles.
From the DE 197 19 503 A1 an apparatus for the chemical-mechanical polishing of surfaces has become known. It includes two polishing stations with vertically movable vacuum chucks for a semi-conductor wafer. The polishing stations have polishing tables which can be rotated about a vertical axis. The vacuum chucks are guided along two parallel horizontally extending guides. By this, two wafers can be polished by a polishing table contemporarily. At least one transfer means for the wafers is provided. Furthermore, on opposing sides of the guides loading and unloading means for the wafers are provided which can be aligned with the vacuum chucks. The transfer means normally are formed by a robot.
During the transportation and the processing the wafers are held by a vacuum chuck or a carrier. This has the task to transfer a homogenous pressure field or different pressure profiles onto the back side of the workpiece. The so-called sharp surface, i.e. the surface which is provided with circuits is facing the polishing table. Usually, the chuck is retained and moved by a corresponding actuating means which rotates the carrier about a vertical axis and moves it along linearly in vertical and horizontal direction.
The throughput through a CMP apparatus is mainly dependent upon the number of polishing stations. On the other side, the processing times for the planarization are relatively short (typically 90 seconds). Due to the short processing times bottlenecks may occur between the individual sections and limit the throughput.
It is an object of the invention to provide an apparatus for the chemical-mechanical polishing of workpieces, in particular of semi-conductor wafers, whereby the complete time of the workpieces within the apparatus can be reduced.
In the invention the loading and unloading station includes a carrier which is supported for rotation about a vertical axis and which is rotated by a rotary driving means. The rotatable carrier has at least two horizontal loading surfaces exposed upwardly. In the apparatus according to the invention further at least two polishing stations are associated with a circumference of the rotatable carrier. Two polishing stations preferably are located on diametrically opposed sides of the carrier. A third polishing station can be provided which has an offset with respect to the first polishing stations about an angle of 90xc2x0. Two transfer means are diametrically opposed to the last-mentioned polishing station. The transfer means is to load and unload the workpieces to and from the loading surfaces.
The CMP processes can be carried out by two or more steps, whereby the workpieces are planarized in different polishing stations. By using different chemical substances and polishing cloths in the different polishing stations, different materials, as for example tungsten, copper or titanium nitrite can be worked under optimized conditions. It is important to minimize the transportation times of the workpieces between the polishing stations as the chemical components of the first step may quickly etch the workpiece. In the apparatus according to the invention, a fast transportation from one polishing station to another can take place. By a quick exchange of the workpieces between the polishing stations, the throughput can be increased and the secondary times can be reduced. By the described configuration of the loading and unloading station according to the invention two or more polishing stations can be interconnected so that a fast exchange between the stations can be achieved. Also with a one step process the throughput time can be reduced since the workpieces can be treated during their transport on the loading surface, e.g. a chemical pretreatment can take place and/or a rinsing or cleaning after the polishing step.
In the present CMP process technology it is usual to clean the workpiece after the first polishing step in order to minimize the described disadvantageous effects or to eliminate these effects. In the already discussed publication DE 197 19 503 or U.S. Pat. No. 6,050,885 it has become known to provide a stationary cleaning means. According to the invention, a cleaning means can be associated with the carrier so that during the transport of the workpiece on the carrier a cleaning can take place. As a consequence, undesired etchings on the workpiece can be effectively prevented by cleaning the workpieces during transportation. Additionally, the so-called cross contamination between the polishing stations in a two step process can be eliminated.
The positioning of the workpieces on the loading surfaces by means of the transfer means normally is such that the workpieces are centered prior to being picked up by a chuck. Therefore, the loading surfaces of the apparatus according to the invention are associated with center means which cooperate with the circumference of the workpiece on the loading surface in order to align the workpiece to a predetermined vertical axis. The vertical axis of the chuck can be also aligned with this axis so that a lowering of the carrier onto the workpiece on the loading surface the chuck can pick up the workpiece in a centered manner.
The chuck for the transport of the workpieces and the cooperation with the polishing tables in the polishing station can be formed in a usual way. Preferably, the workpieces are held by vacuum. For the removing of the workpieces from the chuck an air pressure pulse can be generated after switching off of the vacuum. The movement of the chucks along vertical and horizontal axes has already become known and can be carried out as disclosed by U.S. Pat. No. 6,050,885.
From the mentioned publication, it is also known to provide a linear guide for the chucks, with two chucks being provided for each polishing table. The chucks can be moved along the guide independent from each other. For this case, it is of advantage if the carrier has four loading surfaces, with each two loading surfaces having an axis which is in a plane parallel to the guides if the carrier has a corresponding rotary position. By this, per chuck one loading surface can be provided whereby the throughput of the workpieces upon polishing can be considerably increased, in particular in connection with a two or multiple step planarization process. The positioning of the four loading surfaces preferably takes place in steps of 90xc2x0 or multitude of 90xc2x0.
A cleaning means is associated with the carrier. For this, the carrier can include a central elevation which per loading surface positions a nozzle which is connected to a fluid source. By the nozzle cleaning liquid can be sprayed onto the processed surface of the workpiece. The nozzle can also serve to wet the surface of the workpiece by a suitable liquid. In such an elevation also a number of detectors can be mounted which detect whether a workpiece is on a loading surface.
It is necessary to center the workpieces on the loading surfaces so that they can be picked up by a chuck in a centralized manner. As to this, different known structures can be used. According to an embodiment of the invention, a plurality of centering cams are provided which are located on a circle and which have support surfaces which accommodate a marginal portion of the workpiece. The centering cams further include radially adjustable stop surfaces which may engage the circumference of the workpiece in order to align the workpiece with respect to a predetermined vertical axis. To this purpose, the stop surfaces are synchronously actuated.
The loading surfaces can have a concave shape so that the space between an accommodated workpiece and the loading surfaces can serve as cleaning chamber. It is further possible to drain liquid from this cleaning chamber to one or more bores in the loading surface. Furthermore, a nozzle can be arranged in the loading surface for the supply of cleaning fluid to the described chamber between workpiece and loading surface. Finally, by means of such measures the contact surface of the chuck can be cleaned if it is lowered onto the loading surface.
With the invention a multi function apparatus is created by which through a rotary movement the individual polishing stations and the transfer means could be interconnected in order to decrease the transportation times as short as possible. Furthermore, by means of the multi function apparatus the throughput can be increased, in particular in a two step or multiple step process, wherein different materials as for example tungsten, copper or titanium nitrite is to be processed with different chemical substances and polishing cloths in different polishing stations. By the integration of suitable rinsing and cleaning means, it is possible to avoid etching and chemical reactions which can occur by remainders on the workpieces. Furthermore, the multi function apparatus according to the invention prevents the so-called cross contamination, i.e. the transportation of different materials and chemical components between the polishing stations. Furthermore, the rinsing and cleaning means can be used for a chemical pretreatment of the workpieces in order to prepare the workpieces for the second and third polishing step. Since the cleaning, the pretreatment and the like takes place during the transportation, the throughput speed is not affected.